Trifluoromethyl derivatives of vinyl aromatic compounds



Patented Jan. 14, 1947 U I E ST TES PATENT" orrics 'ramwonomn'mrnDERIVATIVES or VINYL momrrc COMPOUNDS Mary w. Renoll, Dayton,

Ohio, assignor to Monsanto Chemical Company, St. Louia Mo-i acorporation oi Delaware No Drawing. Application April 15, 1844,

Serial No. 531,283

Claims. 1

The present invention relates to nuclear (trifluoro) -methyl derivativesof vinyl aromatic compounds, more particularly to(triiluoromethyl)styrenes,. and to a method of producing the same.

An object oi the present invention is the production of nuclear(trifiuoro)methyl derivatives of vinyl aromatic compounds. Anotherobject of the invention is the preparation of (triiluoro--methyl)styrenes. A further object is the rovision of new polymerizablemonomers for the plastics and coatings industries. Still another objectof the invention is the provision of new polymeric and copolymericresinous materials.

These and other objects which will be hereinafter disclosed are providedby the following in= vention wherein there are prepared new(trifiuoro)methyl derivatives of vinyl aromatic compounds having thefollowing formula:

wherein Ar is an aromatic hydrocarbon radical. As examples of compoundshaving the above-- structure may he mentioned meta-(trifluoromethyl)styrene, ortho- (trifluoromethyl) styrene, para- (trifiuoromethyl)styrene, 1- (trifiuoromethyl)-3 vinylnaphthalene, 1(trifiuoromethyD-dresinous materials that are characterized by a highdegree of thermal stability. They readily undergo copolymerization withother unsaturated materials, for example, styrene or butadienev to giveresinous or rubbery copolymers possessing unusual properties, thepreparation or the rubbery copolymers being the subject 01' my copendingapplication, Serial No. 531,284, filed April 15, 1944, assigned to thesame assignee as the present application.

While I am aware of the previous preparation of other fluorinederivatives of vinyl aromatic hydrocarbons wherein the fluorine iscontained in an aliphatic substituent, for example, thebetatiuorostyrene reported by Swarts (Bull. soc. chim. (4) 25,152),thepresent triiluoromethyiated vinyl aromatic compounds ditIeressentiallyfrom the Swarts compound in that they contain three atoms ofvery stable. bound fluorine, the fluorine being present. in the vinylaromatic compounds in such a manner as todacilitate, rather than hinder,polymerization. fiince chain-substitution in styrene is knownfto detractfrom polyvinylnaphthalene, l-(trifluoromethyl) 2 vinylj naphthalene,4-(trifluoromethyl) -4'-vinylbiphenyl, etc.

Compounds having the abovegeneral formula are readily obtainable byreaction of nuclearly trifluoromethylated aryl magnesium halides withacetaldehyde to yield trifluoromethylated aryl methyl carbinols anddehydration of the latter to give the corresponding trifluoromethylatedvinyl aromatic compounds., substantially according to the followingseries of reactions:

atures, in the presence or absence of catalysts,

they polymerize to give cleanhard, transparent merizing ability, thebeta-fluorostyreneof Swarts is or comparatively little value in thepreparation 01 resinous or rubbery materials. The discovery thatthe(trifiuoromethyl) group when included in a vinyl aromaticnucleus has anaccelerating eflect on polymerization was unexpected.

In preparing by new, trifluoromethvlated vinyl aromatic compounds Iproceed substantially as follows: I prepare a Grignard reagent, forexample, substantially according to the procedure described by Simoneand Ramler (J. Am.

Chem. Soc. 65, 389 (1943)) for the preparation ofmeta-trifluoromethylphenylmagnesium bromide, i. e., by reaction of aunclearly halogenated, nuclearly trifluoromethylated aromatichydrocarbon with magnesium in dry ether. I then slowly add acetaldehydeto the 'Grignard reagent, preferably with vigorous stirring and at lowtemperatures in order to prevent volatilizetion of the aldehyde.Temperatures of from I -10 C. to 20 C. are advantageously employed,

and preferably temperatures 01' from, say -5 C. to 5 0., but thecondensation may be eflected at increased temperature if an excess ofsolvent or suspending agent be employed and the acetaldehydc the vaporstate,

The reaction of the Grignard reagent with acetaldehyde, especially whenemploying the low temperatures noted above, takes place smoothly and ingood yields, which fact is surprising in view oi. the slight reactivityof meta-triiiuoroitrcdluced into the reaction vessel in a,414,sao

methylphenylmagnesium bromide with dimethyl sulfate (for the preparationor meta-methylbenzotriiluoride) as reported by Simone and Reader in thearticle referred to above.

The triiiuoromethyi aryl methyl earbinols thus obtained are readilydehydrated to give the corresponding triiluoromethyl vinyl arylcompounds, and the triiiuoromethyl group is unaffected by thedehydration. Since the trichloromethyl group is very unstable underordinary dehydrating conditions, the stability or the triiluoromethylgroup in a dehydration suchas that which is eiiected, ior example, inthe presence alumina, is surprising.

Dehydration oi the triiiuoremethyl aryi methyl carbinols may be effectedcatalyti'cally in either the liquid or the vapor phase. As catalysts Imay .employ generally inert masses 01' large surface such as ActivatedAlumina, activated charcoal, silica. silica gel, pumice, pumiceimpregnated with aluminum phosphate, activated earths/glass fragments,magnesium oxide, etc. Although the dehydrating step may be effected bysimply refluxing in the liquid phase the carbinol in the presence of acatalyst, and ii desired in the presence of a solvent or diluent, thismethod leads to the formation or some polymeric materiah For optimumyields of the monomeric (triiluoromethyl) vinyl aryl' compounds I preierto conduct the dehydration in the vapor phase. The (trii'luoromethyl)vinyl aryl carbinols may be vaporized and the vapors passed therefromover and through the dehydrating catalysts, Better results are obtainedby flashing the carbinols into a vapor by dropping upon a heatedsurface, in such a manner that the flash evaporation thereof takes placeat pressures below atmospheric, when employing the flash evaporationprocedure, pressures oi irom 30 mm. to 250 mm. pressure absolute, i. e.,from he to about 5 of an atmosphere are preferably used, because morerapid iiow is obtained thereby. Temperatures should be above 250 C., butbelow temperatures at which thermal cracking takes place. Temperaturesin the neighborhood of from 290 C. to 320 C. have been found to givegood yields of the (triiluoromethyl) vinyl aryl compounds.

The invention is further illustrated. but not limited, by the followingexample:

Example Preparation of meta-(trifluoromethubphem l methyl carbinol: .AGrignard reagent was prepared by reaction or 326 g. 01'meta-bromobenzotrifluoride with 3'7 g. of magnesium in 350 cc. of dryether. The reaction vessel containing the 4 product, 8. P. 99' C.-99.5C, at 15 him, u 1.4560; d4" 1.2369.

Preparation 0/ meta- (trifluoromethyl) styrene: Dehydration oi the abovecarbinol was eiiected by passing 479 g. (2.52 mol) of it over ActivatedAlumina at atemperature oi' 290,C.-300 C, and a pressure of from 65 to75 mm. The equipment employed for this purpose comprised a silica tubehaving a length oi about 2 feet and an internal diameter or 0.75 inch.The tube was packed with an Activated Alumina 01 about 4-6 mesh particlesize and the carbinol was passed through it at the rate or about =2drops per second. After the end of the run the reaction tube was washedwith benzene and the benzene washings were added to the dehydrationproduct. Separation of the reaction water was eilected by means or aseparatory tunnel and the benzene was removed by distillation at reducedpressure. The meta-(trifluoromethyhstyrene was distilled at atemperature 0! 78 to 79 C. at a pressure oi 57 mm. oi

mercury. It was obtained in a 79.0% yield. Redistiliaticn gave a purerproduct, B. P. 762 C./55 mm., n 1.4682; d4 1.1588. When cooled in liquidair the meta-(trii'iuoromethyl)styrene became viscous at a temperatureor about -100 C.

and solidifledto a glass-like solid at lower temperatures. 1

Polymerization or the meta-(trifluoromethyl) styrene was effected bymaintaining it for a period or about 18 hours at a temperature 01' 105C. in the absence 0! a catalyst of polymerization. The product was ahard, clear, colorless resin having a melting point of 195 C. and adecomposition point of 210 C. It .was soluble in dioxane, ethanol, ethylacetate, acetone, ethylene dichloride and 2-nitropropane and it wasswollen bybenzene, gasoline and carbon tetrachloride. Films oi the resinprepared by casting solutions of the same were colorless..-

transparent products of very good flexibility and resistance to heat andsunlight.

Meta-(triiluoromethyhstyrene is particularly valuable as acopolymerizing agent in the preparation oi readily milled, synthetic,rubbery materials. A

Ortho-(triiluoromethyllstyrene and para- (triiluoromethyl) styrene areobtained by the procedure described above for the preparation of productwas then immersed in a dry-ice" bath and there was slowly added to it,with vigorous stirring and over a period or 1.75 hours, a mixtureconsisting of 66 g. of acetaldehyde in 80 cc. of dry ether. Duringaddition or the acetaidehyde the temperature of the reaction mixturevaried irom 3 C. to 5 C. The product was then poured into about 1 kg. ofice and treated with about 400 cc. of 15% suliuric acid. The water layerwas'extracted 3 times with ether, and subsequently part of the ether wasremoved from the extract by ordinary distillation. The rest of the etherwas removed by lowering the pressure to 14 mm., at which pressure thecarbinoi was also distilled. The meta-(triiiuoromethyhphenyl methylcarbinol which is thus obtained in about 80% yield has a boiling pointof 97" C. at 14 mm., and redistiilation oithis gave a purermeta-(triiluoromethyl) styrene, employing orthobromobenzotriiluoride orpara-bromcbenzotrifluoride, respectively, instead of the meta-bromocompound for the preparation oi the Grignard reagent.

Since bromination oi benzotriiluoride yields, as

the -mono-bromo-substituent, the meta-bromo derivative exclusively, thepreparation 01' orthoand para-Ktrifluoromethyl)phenyl methyl carbinolfrom the Grignard reagent is complicated by th fact that the initialbromc compounds must be prepared indirectly. Ortho-bromobenzotrifluorideis obtainable by the Sandmeyer reaction from theortho-aminobenzotrifluoride reported by Rouche (Bull. sci. Acad. roy.Belg. 13, 346-57 (1927)). Para-bromobenzotrifluoride is obtainable byreducing Rcuche's para-nitrobenzotrifluoride to the corresponding aminocompound and then converting the para-aminobenzotrifluoride to the bromocompound by the Sandmeyer reaction.

While bromination oi benzotriiluoride yields only the meta-bromoderivative chlormation oi benzctrifluoride yields large quantities ofmetachlorobenzotrifluoride, some ortho-chlorobenzotriilucride and verysmall quantities oi parachlorobenzotrifiuoride. In order to avoid thenecessity of preparing the orthoand parabromobenzotrifluorides by anindirect method, I have attempted to prepare the carbinols by using thecorresponding chloro-compounds in making the Grignard reagents. Whilethe (trifluoro- 'methyDphenyl magnesium chlorideswere found the(trifluoromethyl)vinylbiphenyls are obtain able by the general proceduredescribed above for the preparation of the (trifiuoromethyl)styrenes.

Since from the foregoing description of the invention it will beapparent to those skilled in the art that various other embodiments ofthe invention may be made without departing from the spiritand scopethereof, it is to be understood that no limitations are intended exceptthose which are specifically recited in the following claims:

What I claim is:

1. As a new product a compound of the general formula:

CHmCHAnCF:

wherein Ar is an aromatic hydrocarbon radical. 2. As a new product acompound of the general formula:

3. Meta-(trifluoromethyl) styrene. 4. Ortho- (trifluoromethyl) styrene.5. Para-(trifluoromethyl) styrene.

6 6. A polymer of the compound defined in claim 1.

'7. A polymer of the compound defined in claim 2.

8. Polymeric meta-(trifluoromethyDstyrene.

9. The process for the preparation of nuclearly substituted(trifluoromethyl) derivatives of vinyl aromatic hydrocarbons whichcomprises treating a compound of the general formula:

JWIQ-ALCI":

wherein x is halogen and Ar is an aromatic hydrocarbon radical, withacetaldehyde to form a carbinol of the general formula:

OH .OH.Ar.OFs

wherein Ar is an aromatic hydrocarbon radical, separating the carbinolso obtained and subjecting it to catalytic dehydration.

10. The process'for the preparation of nuclearly substituted(trifluoromethyl) derivatives of styrene which comprises treating acompound of the general formula: I

wherein xis halogen, with acetaldehyde to form a carbinol of the generalformula:

OBOE-CHI then separating the carbinol so obtained and subiecting ittocatalytic dehydration.

MAR-Y W. mom

